The identification of critical periods during childhood and adolescence for bone fracture is of great importance to pediatric medicine. Fracture risk in healthy children is at its peak during the pubertal growth spurt, and in recent years, the incidence of fracture has increased by over 30%. The pubertal growth spurt is characterized by significant increases in the length of long-bones as well as periosteal expansion of the bone shaft. Because the integrity of the skeleton to resist fracture depends upon the cross-sectional geometric design of the bone (distribution of cortical bone) and the quality/composition of the bone tissue represented in that geometry (bone mass), the co-variation of these components of bone strength during peak times of growth or rapid maturation must be fully understood. The primary goal of the proposed study is to determine the impact of maturational events (peak height velocity, menarche, skeletal maturity) on relationships between gross bone geometry and measures of bone mass during childhood and adolescence, with specific reference to fracture history in our cohort. This goal will be accomplished using radiographic data collected under the PI's previous grants (R01HD56247 and R01AR055927) and collecting density data available from the same serial radiographs of over 500 children (median of 5 radiographs per child). We propose to test hypotheses regarding the covariation of bone cross-sectional geometry and bone mass, and to characterize the behavior of this covariation vis--vis specific maturational events.